The travelling Copenhagen fans had to seek refuge under the stands after being attacked by what appeared to be supporters of the Ukrainian club and the start of the second half was delayed by 15 minutes.

UEFA told The Associated Press that it "received the report this morning and an investigation has been opened against Dnipro Dnipropetrovsk for crowd disturbance and insufficient organisation."

The matter will be decided on Aug. 14, at UEFA's next disciplinary meeting. The return match is scheduled for Aug. 6.

Dnipro fans have said they were provoked by a Russian flag being waved by Copenhagen fans -- which has been vehemently denied by the Danish club and its fan association.

In a statement, the club said that fans were body searched and their flags and banners checked by both FC Copenhagen people and local security people and "no Russian flags were found." Also, none of the local, UEFA or Danish security people on the site saw any Russian flag, the statement said.

"This is an unacceptable security breach that simply cannot take place either in Danish or European stadiums," Copenhagen said in a statement.

The Ukrainian army is fighting with pro-Russia separatists in the east of the country. UEFA has decided that Russian and Ukrainian teams cannot be drawn against each other but is allowing matches to take place in the countries, although it ordered that the match against Copenhagen take place in Kiev.